A manually tightened drill chuck is a commonly used tool in daily life, and mainly it is used for boring and drilling holes when installing or fixing articles. If a manually tightened drill chuck is not provided with a self-locking mechanism, as shown in FIG. 1, the drill's forceful vibrations in the course of use can easily cause the drill bit on the front end to loosen, affecting the bore quality, or, in severe cases, to break, which is dangerous.